4.7 FAPI

Here's a 4.7 FAPI for you:

  return array('robotstxt' => array('#type' => 'textarea',
                                    '#title' => t('Value for robots.txt'),
                                    '#default_value' => variable_get('robotstxt', ''),
                                    '#cols' => 60, '#rows' => 20, '#required' => false));

The default value from 4.6 was an unset $robotstxt var, so I switched it here since init() looks like it takes care of making sure it's set all the time.